MC leaves ML's world after he confirms that ML won't have any problems and before he deepens his love towards ML too much. He was afraid that if he stayed even a lil more, he won't be able to move on from that world. In the end, system removed the memory of MC's existence from the world. Even ML forgot him, but the instinct ML had towards MC remained. ML still followed the path he had decided after listening to MC's interests, kept the b'day gift given to him by MC even though it was a large doll that seemed useless and he still felt as if there was once a 'seatmate'. He becomes old... he had all but still felt he had nothing.

The system as before was supposed to be erasing memories of all. But ML somehow retained his memory. He remembered the MC. It was so sad watching ML trying to find traces of MC in the world.

The ML and MC are in interstellar era in real world. MC is a spiritual therapist (it was MTLed as Mental Doctor *cough*) and ML is someone who got Calamity (sometimes MTLed as Disaster) [an energy being filled with negative emotions against humans but wants a human form & tries to occupy a human body] and MC tries to heal ML's spiritual world trying to prevent Calamity from taking over his body.

ML and MC already knew each other before, so there won't be a drama of "it all happened in another world/dream.", etc.

he leave the plane and the ML get his memories erased but still does things subconsciously like he did when he was with the MC. It really made my chest throbಥ╭╮ಥ when his head hurt when he tried to remember theMc